From the past, as one type of contact lens, an item is known that has multiple power regions with mutually different lens powers set in the optical region. For example, with a contact lens for correcting presbyopia, since the lens power required for near vision and the lens power required for far vision differ, contact lenses provided with a near sight region for which a lens power for near vision is set and a far sight region for which a lens power for far vision is set are prescribed for correction of presbyopia. In specific terms, as disclosed in Patent Document 1 (Japanese Unexamined Patent Publication No. JP-A-561-272717), a contact lens is known having a structure for which the near sight region and the far sight region are formed in concentric circles in relation to the lens geometric center.
However, in a worn state with the contact lens overlapped on the cornea of the eye, the pupil center which is positioned on the center axis of the eye optical system is often shifted from the geometric center of the contact lens. Possible reasons for this include that since the curvature distribution of the corneal surface of the human eye is not uniform, it is easy for the contact lens to stabilize shifted to the ear side, or for the pupil center to be in an eccentric position to the nose side in relation to the geometric center of the cornea.
In this way, in a worn state, when the pupil center is shifted from the geometric center of the contact lens, as noted in Patent Document 1 noted above, with a contact lens of a conventional structure for which a near sight region and a far sight region are provided concentrically with the lens geometric center, there was the problem that it was difficult to obtain sufficient quality of vision (QOV). In light of that, this applicant proposed a decentered type contact lens for which the optical center axis of the optical region is made to deviate to the nose side from the lens geometric center with Japanese Unexamined Patent Publication No. JP-A-H06-289329 (Patent Document 2). With this contact lens noted in Patent Document 2, it is possible to suppress the distance between the pupil center and optical center axis in a worn state, and to obtain an improved QOV.
However, as noted in Patent Document 2, in regards to the decentered type contact lens, when the inventor did additional investigation, they found that there are cases when it is difficult to stably obtain sufficient effect in terms of improved QOV, and that there was still room for improvement.